Copolymers having gem-bisphosphonate groupings

ABSTRACT

A copolymer includes a main hydrocarbon chain and side groups including carboxylic groups and polyoxyalkylate groups. The copolymer further includes gem-bisphosphonate groups. The copolymer can be included in an admixture for suspensions of mineral particles and in a composition of mineral particles. The copolymer can also be used for fluidifying and maintaining fluid, suspensions of mineral particles and for reducing the sensitivity of hydraulic compositions to clays and alkaline sulfates.

PRIORITY AND CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser. No. 14/111,752, filed Oct. 14, 2013 and published as US 2014/0039098 A1 on Feb. 6, 2014, which is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/EP2012/056840, filed Apr. 13, 2012, designating the U.S. and published as WO 2012/140235 A1 on Oct. 18, 2012, which claims the benefit of French Patent Application No. FR 11 53312, filed Apr. 15, 2011. All applications for which a foreign or a domestic priority is claimed are identified in the Application Data Sheet filed herewith and are hereby incorporated by reference in their entirety under 37 C.F.R. § 1.57.

FIELD

The present invention relates to copolymers with gem-biphosphonate groups, to a method for their preparation and to their use as fluidifiers of suspensions of mineral particles, notably compositions of cements and plaster formulations.

STATE OF THE ART

Generally, admixtures are added to cement compositions for improving their properties. Rheological properties and their change over time, related to their workability, are among the fundamental properties of cement compositions.

Fluidifiers or plasticizers are in particular used, which have the effect of fluidifying cement compositions and thus allow a reduction in the amount of water added, this is why they are also designated as water reducing agents. The composition then has a higher density and results in a material having a higher mechanical strength.

Certain soluble polymers called superplasticizers give the possibility of further reducing the amount of water. Superplasticizers of the type of polyalkoxylated polycarboxylic acids (PCPs) are notably known.

Document FR 2892420 describes superplasticizers with phosphonate and polyoxyalkylate groups for fluidifying suspensions of mineral particles, in which the phosphonate groups are amino-bisalkylenephosphonic groups of the following formula (A):

wherein L represents a group for binding to the main chain and X is an alkylene or oxyalkylene group. Phosphonate monomers may notably be obtained by diphosphonation according to the conditions of the MOEDRITZER-IRANI reaction by reaction of an amine with formaldehyde and phosphorous acid.

In order to access these structures, chemical modification of a polymer by post-grafting is also proposed. This method includes two steps, i.e. the copolymerization of an unsaturated carboxylic acid with a polyethoxylated (meth)acrylic ester followed by grafting of a phosphonate amine or alcohol synthon or, alternatively, polymerization of the unsaturated carboxylic acid and subsequent esterification with polyalkoxylate compounds followed by grafting of a phosphonate synthon.

Technical Problem

The object of the invention is to provide novel modified copolymers useful as admixtures for suspensions of mineral particles.

Another object is to provide a method for preparing these copolymers which is simple and economical and in particular does not require the use of formaldehyde.

Still another object is to provide admixtures for suspensions of mineral particles having substantial water reducing power, good maintenance of rheology, low sensitivity to alkaline sulfates and to clays and good robustness towards different cements.

SUMMARY OF THE INVENTION

The objects mentioned above are achieved according to the invention with copolymers including gem-biphosphonic groups.

Thus, according to the invention a copolymer is provided, comprising a main hydrocarbon chain and side groups, wherein the side groups comprise carboxylic groups, polyoxyalkylate groups and gem-biphosphonate groups.

According to a second aspect, the invention is directed to a method for preparing these copolymers comprising the steps:

-   -   (i) polymerizing a monomer bearing a carboxylic group,         optionally in the presence of a monomer bearing a         polyoxyalkylate group; and     -   (ii) grafting the obtained polymer with a reactive         gem-biphosphonate compound.

The gem-bisphosphonate copolymer thereby obtained is advantageously formulated before use, preferably as a solution, notably as an aqueous solution. The formulation may also include the customary additives in this field.

According to another aspect, the invention is therefore directed to an admixture for suspensions of mineral particles comprising the copolymer according to the invention as a solution in a suitable solvent or in a dry form, notably as a powder.

Moreover, the invention according to another aspect is directed to the use of the copolymer according to the invention for fluidifying suspensions of mineral particles and/or for maintaining the workability of hydraulic binders. It is also directed to the use of the copolymer according to the invention for reducing the sensitivity of hydraulic compositions to clays and alkaline sulfates.

Finally, according to a last aspect, the invention is directed to a composition of mineral particles comprising the copolymer according to the invention.

Definitions

Within the scope of the present discussion, by the term of «suspension of mineral particles» or «hydraulic composition» is meant any binder with hydraulic setting, i.e. notably in addition to cements such as Portland cements, aluminous cements, mortars further comprising fine granulates, concretes further comprising coarse granulates or further anhydrous calcium sulfate or semi-hydrates thereof. The term also encompasses inert mineral fillers such as calcium sulfate dihydrates as well as calcium carbonate, silica, titanium hydroxide and clay compounds.

By the term of «hydrocarbon chain» is meant an aliphatic, saturated or unsaturated, aromatic, arylalkyl or alkylaryl, linear or branched group, including carbon and hydrogen atoms, optionally interrupted and/or terminated with one or several hetero-atoms such as S, O, N, P.

The term of «gem-bisphosphonate group» is meant to refer to groups including two phosphonate groups bound to a same carbon atom. These groups therefore have a P—C—P bond.

By the term of «alkyl group» is meant a linear, branched or cyclic alkyl group.

In the same way, by the term of «alkylene group» is meant a linear or cyclic alkylene group.

DETAILED DESCRIPTION OF THE INVENTION

The copolymers according to the invention are comb copolymers including a main hydrocarbon chain on the one hand and side groups on the other hand. They are further characterized by the presence of carboxylic groups, polyoxyalkyl groups and gem-bisphosphonate groups as side groups.

The simultaneous presence of these three types of groups gives the copolymer interesting properties as an admixture, notably of a superplasticizer, for suspensions of mineral particles.

[Copolymers]

In their widest definition, the copolymers proposed according to the invention are modified polymers of the PCP type including gem-bisphosphonate groups.

The polymer is of the comb type, including a main chain and side groups. The main hydrocarbon chain preferably does not comprise any hetero-atoms. A linear main chain is more preferred.

According to the invention, the copolymer moreover comprises side groups including carboxylic groups and polyoxyalkylate groups, and further gem-bisphosphonate groups. Advantageously, the polyoxyalkylate side groups are bound to the main chain through an ester, ether or amide bond.

Preferably, the gem-bisphosphonate groups fit the formula (IA) below:

wherein:

L represents a group for binding to the main chain, in particular a bond, an oxygen atom, a group —NR₄—, (R₄ being hydrogen or a C₁-C₆ alkyl group), or an alkylene group, preferably, L is an oxygen atom or a group —NR₄—;

X is a spacer group, in particular a C₁-C₂₀ alkylene group optionally substituted or a chain of groups of formula -(QO)_(n)— in which Q represents an alkylene group with 2 to 4 carbon atoms or a mixture of alkylene groups, n being an integer varying from 1 to 500, preferably, X is a C₁-C₆ alkylene group;

R1 is, independently of each other, a monovalent group, notably a hydrogen, a C₁-C₆ alkyl group or a group of formula -(QO)_(n)R₅ wherein Q represents an alkylene group with 2 to 4 carbon atoms or a mixture of these alkylene groups, n is an integer varying from 1 to 500 and R₅ is a hydrogen or a C₁-C₃ alkyl, or R1 is a cation, notably an alkali metal, alkaline earth metal or ammonium cation; and

R2 is a monovalent group, notably a hydrogen atom or a hydroxyl group or a C₁-C₁₀ alkyl group, preferably, R2 is a hydroxyl group.

The group L is most often bound to a carboxylic group of the copolymer and consequently the oxygen atom forms therewith an ester function and the amine groups, an amide function.

The proportion of the respective gem-bisphosphonate groups in the copolymer according to the invention may widely vary. In particular, the copolymers comprise 0.1 to 60%, in particular 1 to 40% and most particularly 2 to 10% in number of gem-bisphosphonate side groups.

The copolymer also includes as side groups, polyoxyalkylate groups. These polyoxyalkylate groups may be bound to the main chain directly or via groups formed with the present carboxylic functions, notably through an ester or amide bond.

They may also be integrated into the gem-bisphosphonate groups, notably of formula (I).

The polyoxyalkylate groups may notably be of the formula (II) below: -R _(e)-Z-A  (II)

wherein:

R_(e) is a C₁-C₁₂ alkylene group or a 0=0 group or is further absent; and

Z is an oxygen atom or a group N—R⁴, R⁴ being hydrogen or a C₁-C₆ alkyl group; and

A is a group of formula -(QO)_(n)—OR³ wherein:

-   -   Q represents an alkylene group with 2-4 carbon atoms or a         mixture of these alkylene groups;     -   n is an integer varying from 1 to 500; and     -   R³ represents a hydrogen atom or a C₁-C₁₂ alkyl, aryl, alkyaryl         or arylalkyl group, preferably a methyl.

The copolymer generally comprises 0.001 to 80% in number, in particular, 10 to 50% in number of polyoxyalkylate groups.

According to the invention, the copolymer moreover includes carboxylic groups.

Preferably, the carboxylic groups fit the formula (III) below: —C(O)—O-R _(d)  (III)

wherein:

-   -   R_(d) represents H or a C₁-C₁₂ alkyl, aryl, alkylaryl or         arylalkyl group or an alkali metal, alkaline earth metal or         ammonium cation.

The proportion of the carboxylic groups in the copolymer may vary from 0 to 90%, in particular from 40 to 80% in number of carboxylic groups.

These carboxylic groups may be in the form of a non-dissociated acid. Most often, they will however be at least partly or totally neutralized, esterified or amidified.

The copolymer according to the invention generally has an average molar mass comprised between 1,000 and 220,000 (Mw), preferably between 10,000 and 110,000 (Mw) as determined by SEC («size exclusion chromatography») in equivalent of standard polyoxyethylene.

The polymolecularity index Ip is preferably comprised between 1 and 5, preferably between 1.5 and 3.

Method for Preparing the Copolymers According to the Invention

According to a second aspect, the invention proposes a method for preparing the copolymer grafted with gem-bisphosphonate groups as described below.

Several types of reaction may be suitable for preparing the copolymer according to the invention.

Notably, it may be prepared by copolymerization of suitable monomers or by modifying a polymer by grafting side groups. The latter method is also called post-grafting.

Thus, according to an embodiment, the described copolymer is prepared by bulk or solution copolymerization, in the presence of a suitable catalyst, of monomers which may polymerize bearing the sought groups respectively. It is thus possible to polymerize a mixture comprising a monomer bearing a gem-bisphosophonate group, a monomer bearing a carboxylic group and optionally a monomer bearing a polyoxyalkylate group.

A suitable monomer bearing the gem-bisphosphonate group is notably a (meth)acrylate or (meth)acrylamide bearing a gem-bisphosphonate unit, for example, obtained by reaction of a compound of formula of (I) with (meth)acryloyl chloride or (meth)acrylic anhydride.

A monomer bearing a suitable polyoxyalkylate group is notably (meth)oxypolyethylene glycol, (meth)acrylate or (meth)acrylamide.

The monomer bearing a carboxylic group may in particular be selected from unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid and their substituted derivatives, or further a compound which may generate unsaturated carboxylic functions in situ, like maleic anhydride.

The copolymer according to the invention may then be obtained by copolymerization of these monomers, notably via a radical route under the usual conditions in the presence of a suitable initiator.

According to another embodiment, the polymer is prepared with a so-called «post-grafting» method. In this method, a polymer comprising a hydrocarbon chain and the carboxylic side groups and optionally polyalkoxylate side groups is modified by grafting gem-bisphosphonate groups.

Grafting is preferably carried out by reacting carboxylic groups with a gem-bisphosphonate compound bearing a reactive function, notably a primary or secondary amine or alcohol group.

Also, according to a second aspect, the invention is directed to a method for preparing the copolymer described above comprising the steps:

-   -   (i) polymerizing a monomer bearing a carboxylic group,         optionally in the presence of a monomer bearing a         polyoxyalkylate group; and     -   (ii) grafting the obtained polymer with a reactive         gem-bisphosphonate compound.

Alternatively, it is possible to polymerize the carboxylic monomer and then esterify to the desired degree the carboxylic groups with polyoxyalkylate compounds, as this is for example described in patent application FR 2 776 285, before grafting the obtained product with a reactive gem-bisphosphonate compound.

Preferably, the reactive gem-bisphosphonate compound is a gem-bisphosphonate alcohol or amine, amines being preferred because of their better reactivity at a low temperature.

Advantageously, the reactive gem-bisphosphonate compound is of the following formula (I):

wherein:

Y is a functional group which may react with the carboxylic functions of the polymer, notably a hydroxyl, primary or secondary amine, isocyanate or thiol group;

X is a spacer group, in particular a C₁-C₂₀ alkylene group optionally substituted or a chain of groups of formula -(QO)_(n)— in which Q represents an alkylene group with 2 to 4 carbon atoms or a mixture of these alkylene groups, preferably, X is a C₁-C₆ alkylene group, n being an integer varying from 1 to 500;

R1 is, independently of each other, a monovalent group, notably a hydrogen, a cation, notably an alkali metal, alkaline earth metal or ammonium cation or a C₁-C₆ alkyl group and preferably a C₁-C₃ alkyl group; and

R2 is a monovalent group, notably a hydrogen, a hydroxyl or a C₁-C₁₀ alkyl, preferably R2 is a hydroxyl group.

The polymer to be grafted will not necessarily include polyoxyalkylate groups from the moment that the gem-bisphosphonate compound includes polyoxyalkylate groups.

The grafting reaction may advantageously be conducted at a temperature above 120° C., preferably between 150 and 200° C., and in particular between 170 and 180° C. The water formed by the reaction is then removed from the reaction mixture by evaporation and the reaction product is recovered as a dry residue.

The carboxylic or phosphonic groups present in the reaction product may then be totally or partly neutralized.

[Admixture]

According to a further aspect, the invention proposes an admixture for suspensions of mineral particles, comprising the described copolymer.

In order to facilitate the application and dosage thereof, the admixture may be formulated as a solution in a suitable solvent.

Preferably, the suitable solvent comprises or consists of water. In certain cases, the use of another solvent, such as an alcohol or a glycol may be contemplated, additionally or alternatively, for example in order to facilitate solubilization.

The concentration of polymer in the admixture mainly depends on the contemplated application. Generally, the admixture comprises from 1 to 50, preferably 10 to 30% by weight of polymer based on the total weight.

Alternatively, the admixture may also appear in dry form notably as a powder.

The formulation of the admixture may moreover comprise other usual additives, such as anti-foam agents, accelerators, retardants, water-repellent agents, de-aerating agents, other dispersants, air entraining agents or stabilizers of anti-foam agents.

[Use of the Copolymers According to the Invention]

According to a fourth aspect, the invention provides the use of the admixture for fluidifying suspensions of mineral particles and for maintaining the workability of hydraulic binders.

As hydraulic binders, mention may be made in particular of cement compositions and notably concretes notably pre-fabricated concretes and ready-to-use concretes. These concretes may notably be intended for the building and civil engineering industry.

The amount of admixture to be added to the suspension of mineral particles of course depends on the sought properties and on the contemplated application. It is observed that for the preferred compositions of the invention, this dosage on the other hand varies little with the nature of the medium, and in particular, little with the chemical composition of the cements used.

Generally, for a cement composition, an admixture dosage from 0.01 to 2%, preferably from 0.05 to 1% and most particularly from 0.1 à 0.5% by weight of polymer based on the weight of the cement is suitable for most standard applications.

As an indication, an effective dosage of admixture for preparing a ready-to-use concrete composition is from 0.7 to 1.5% of a 20% dry extract weight formulation based on the weight of cement.

The action mechanism of the described polymers is not entirely understood, it being understood that that of superplasticizers in cement is still not fully elucidated in a general way.

However, it is assumed that the fluidifying effect of the superplasticizers mainly results from repulsion forces set into play between the copolymers absorbed on the surface of the grains.

The combined presence, in the copolymers with gem-bisphosphonate groups according to the invention, of long polyoxyalkylate chains having a dispersion effect and of phosphonate groups having strong capability for complexation and an exceptional absorption power towards di- or tri-valent cations such as calcium or aluminium cations, is assumed to be the reason for the particular properties as an admixture.

Moreover, it was surprisingly observed that the gem-bisphosphonate copolymers according to the invention have an excellent water reducing power/rheology maintenance compromise over a large range of concentrations of polyoxyalkylate chains.

It was further observed that the copolymers according to the invention have low sensitivity to the alkaline sulfates notably present in cement.

Indeed, the conducted tests have shown that functionalization of the PCPs by gem-bisphosphonate synthons gives the possibility of perturbing the adsorption of sulfate ions at the surface of the cement particles and therefore promoting that of the functionalized copolymer and consequently its dispersant action.

This adsorption strongly decreases in the case of high sulfate ion contents as a result of the adsorption competition on the surface of the cement grains, between sulfate ions and the copolymer. Thus, high contents of soluble sulfates generally lead to a low reduction of water, probably due to a lower initial adsorption of the copolymer. However, better workability of the compositions is observed most often, which presumably is related to better availability of the copolymer in the interstitial liquid which gives the possibility of extending the dispersant effect.

Moreover, the copolymer according to the invention advantageously has low sensitivity to the clays often present in sands and limestone fillers making up the suspensions of mineral particles.

Indeed, the presence of clays in the hydraulic compositions affects the efficiency of the superplasticizers because of their adsorption on the surface of these clays and of the insertion of their polyethoxylated grafts into the interfoliar spaces of these clays. Decrease in the maintaining of fluidity then requires an increase in the admixture dosage, which in turn generates costs and beyond which degradation of other properties may be caused, such as the compression strength and durability of the material and which may moreover lead to the occurrence of cracks.

It is assumed that this advantageous effect is related to the fact that the presence of gem-bisphosphonate groups in the copolymers according to the invention increases their affinity for the surface of the cement grains to the expense of that of the clay particles. This phenomenon may be due to the provision of additional anionic charges, related to the substitution of a carboxylate group with 4 phosphonate functions, which makes the approach towards the clays more difficult and therefore the adsorption at their surface.

The obtained grafted copolymers as described above are of particular interest as plasticizers for suspensions of mineral particles, notably of cement compositions and plaster formulations.

Indeed, they have:

-   -   high water reducing power,     -   insensitivity to the alkaline sulfates of the cements,     -   decrease in the sensitivity to clays present in the sands,     -   very good fluidifying power of hydraulic compositions with very         good retention of fluidity.

[Compositions of Mineral Particles]

Finally, according to a last aspect, the invention is directed to a composition of mineral particles comprising the copolymer according to the invention.

The compositions thus with an admixture have prolonged workability with low dosage, including in the presence of high contents of alkaline sulfates and/or clays. Consequently they are of interest for a wide range of applications, in particular ready-to-use concretes, self-compacting concretes, high or ultra high performance concretes (HPC or UHPC) or precast concrete.

The invention will be better explained with reference to the examples which follow, given as non-limiting examples.

EXAMPLES

A. Preparation of the Bis-Phosphonate Synthon

Example 1 Preparation of 1-hydroxyethylene-1,1-bisphosphonic acid (HEDP)

In a 1,000 mL three-neck flask, provided with magnetic stirring, surmounted with a condenser and with nitrogen inertization and placed in a thermostated oil bath and connected to a vacuum pump, 60 g (1 mole) of acetic acid, 123 g (1.5 moles) of phosphorous acid and 500 mL of anhydrous chlorobenzene are loaded. The mixture is brought to a temperature of 100° C. with stirring. The formation of a homogenous solution is observed. 206 g (1.5 moles) of phosphorus trichloride (PCl₃) are then slowly added into the medium. The reaction mixture is maintained at 100° C. for a further three hours and then left to cool at room temperature. The solid residue obtained is washed with chlorobenzene and then dissolved in 500 mL of water and brought to boiling with reflux for 1 hour. After cooling, the solution is treated with active carbon and then filtered. The raw acid precipitates by adding an excess of hot methanol and after separation, the product is recrystallized from one liter of water at 100° C.

The yield is 87% of 1-hydroxy ethylene-1,1-bisphosphonic acid. The reaction product is characterized with ³¹P NMR (CDCl₃), ¹H NMR (CDCl₃) and ¹³C NMR.

Example 2 Preparation of 1-hydroxy-3-amino-propylene-1,1-bisphosphonic acid (AHP)

In a 1,000 mL three-neck flask provided with magnetic stirring, surmounted with a condenser and with nitrogen inertization and placed in a thermostated oil bath and connected to a vacuum pump, 91 g (1 mole) of 3-aminopropionic acid, 123 g (1.5 moles) of phosphorous acid and 500 mL of anhydrous chlorobenzene are added. The mixture is brought to a temperature of 100° C. with stirring. The formation of a homogeneous solution is observed. 206 g (1.5 moles) of phosphorus trichloride (PCl₃) are then slowly introduced into the medium. The reaction mixture is maintained at 100° C. for a further three hours and then left to cool at room temperature. The obtained solid residue is washed with chlorobenzene and then dissolved in 500 mL of water and brought to boiling with reflux for 1 hour. After cooling, the solution is treated with active carbon and then filtered. The raw acid precipitates by addition of an excess of hot methanol and after separation, the product is recrystallized from one liter of water at 100° C.

The yield is 82% of 1-hydroxy-3-amino-propylene-1,1-bisphosphonic acid. The reaction product was characterized with ³¹P NMR (CDCl₃), ¹H NMR (CDCl₃) and ¹³C NMR.

Example 3 Preparation of 1-hydroxy-4-amino-butylene-1,1-bisphosphonic acid (BHP)

In a 1,000 mL three-neck flask provided with magnetic stirring, surmounted with a condenser and with nitrogen inertization and placed in a thermostated oil bath and connected to a vacuum pump, 105 g (1 mole) of 4-aminobutyric acid, 123 g (1.5 moles) of phosphorous acid and 500 mL of anhydrous chlorobenzene are loaded. The mixture is brought to a temperature of 100° C. with stirring. The formation of a homogeneous solution is observed. 206 g (1.5 moles) of phosphorus trichloride (PCl₃) is then slowly introduced into the medium. The reaction mixture is maintained at 100° C. for a further three hours and then left to cool at room temperature. The obtained solid residue is washed with chlorobenzene and then dissolved in 500 mL of water and brought to boiling with reflux for 1 hour. After cooling, the solution is treated with active carbon and then filtered. The raw acid precipitates by addition of an excess of hot methanol and after separation, the product is recrystallized from a liter of water at 100° C.

The yield is 77% of 1-hydroxy-4-amino-butylene-1,1-bisphosphonic acid. The reaction product was characterized by ³¹P NMR (CDCl₃), ¹H NMR (CDCl₃) and ¹³C NMR.

B. Modification of a Polymer by Grafting the Gem-Bisphosphonate Synthon

After obtaining a non-functionalized reference phosphorus-containing copolymer (Example 4), tests for grafting the phosphonate synthon conducted with HEDP are presented in order to determine the best operating conditions (examples 5A-5C). These grafting conditions were then used for grafting HEDP, AHP and BHP synthons at different levels (Examples 6A-6C, 7A-7C et 8A-8C).

Example 4 Preparation of a Reference Polyalkoxylated Polycarboxylic Copolymer

In a 500 mL two-neck flask provided with magnetic stirring, surmounted with a condenser and with nitrogen inertization and placed in a thermostated oil bath, 73.57 g (323.4 mmoles) of polymethacrylic acid (TP 941, marketed by COATEX, acid index 181.1 mg KOH/g) are loaded and then 0.48 g (5.95 mmoles) of soda (aqueous solution with 50% by weight of NaOH) are introduced. One then proceeds with loading 34.35 g (46 mmoles) of methoxypolyethyleneglycol (MPEG) with a molar mass of 750 g/mol and then with 91.60 g (46 mmoles) of methoxypolyethyleneglycol (MPEG) with molar mass 2,000 g/mol and the temperature of the reaction medium is brought to 175° C. When the temperature of the reaction medium attains 100° C., the reactor is put under partial vacuum (<20 mbars).

The moment when the reaction medium becomes homogeneous is taken as TO, the time of the beginning of the reaction. The esterification reaction is left to continue for 7 hours at 175° C. before allowing the reaction medium to return to room temperature.

An anhydrous base is obtained having a comb copolymer mass of 147.5 g i.e. 73.8% based on the initial reaction mixture.

Examples 5A-5C

Optimization of the Grafting Conditions of the Phosphonate Synthon

In order to evaluate the effect of the reaction conditions on the grafting of the polycarboxylic acid, Example 4 was repeated by varying the moment when the gem-bisphosphonate reagent HEDP is introduced, as prepared in the previous examples.

In Example 4, the reaction is conducted without adding any gem-bisphosphonate synthon so as to be used as a reference. In the Examples 5A, the gem-bisphosphonate synthon (HEDP) is added at the beginning of the reaction, when the reaction medium becomes homogeneous (TO) and 4 hours after this moment, respectively.

The reaction mixtures from these reactions are analyzed in terms of acid index and of residual MPEG content by GPC according to the following procedure.

In a first phase, MPEG standards with increasing concentrations are injected and then the corresponding areas are determined. Measurement of the area of the MPEG peak of the sample to be analyzed gives the possibility of accessing the residual MPEG level. The injections are accomplished at 40° C., the columns used are Aquagel Guard OH 8 μm (marketed by Agilent Technologies) positioned in series with two Aquagel OH30 columns (also marketed by Agilent Technologies).

TABLE 1 Conditions of the reaction according to Examples 5A-5C HEDP Amount Acid Reaction [molar index Residual EXAMPLE mixture %] Introduced IA Polyox. 4 Methacrylic — N/A 20.384 3.87% (EPB 662054) acid MPEG 5A Methacrylic 4 At the 36.741 29.84% (EPB 662055) acid MPEG start 5B Methacrylic 4 At T0 33.424 27.88% (EPB 662056) acid MPEG 5C Methacrylic 4 At T0+4 h 33.769 3.83% (EPB 662058) acid MPEG

The results are summarized in the table 1 above

It is seen that the simultaneous introduction of the gem-bisphosphonate synthon with the polyalkoxylated compounds perturbs the esterification reaction.

Deferred introduction into the reaction medium on the other hand, for example after 4 hours of reaction, gives the possibility of again finding an MPEG grafting level equivalent to that of the reference reaction without any phosphonate synthon.

These operating conditions are the ones which were retained for the subsequent study.

Example 6A-6C Preparation of Copolymers of the PCP Type Grafted with HEDP

In a 500 mL two-neck flask provided with magnetic stirring, surmounted with a condenser and with nitrogen inertization and placed in a thermostated oil bath, 73.57 g (323.4 mmoles) of polymethacrylic acid (TP 941, marketed by COATEX, acid index 181.1 mg KOH/g) are loaded and 0.48 g (5.95 mmoles) of soda (aqueous solution with 50% by weight of NaOH) are then introduced. It is then proceeded with the loading of 34.35 g (46 mmoles) of methoxypolyethyleneglycol (MPEG) with a molar mass of 750 g/mol and then with 91.60 g (46 mmoles) of methoxypolyethyleneglycol (MPEG) with a molar mass of 2,000 g/mol and the temperature of a reaction medium is brought to 175° C. When the temperature of the reaction medium attains 100° C., the reactor is set under partial vacuum (<20 mbars).

The moment when the reaction medium becomes homogeneous is taken as TO, the time of the beginning of the reaction. After 4 hours of baking at 175° C., 4.11 g of bisphosphonate synthon according to Example 1 are introduced very slowly and the esterification reaction is left to further continue for 3 hours at 175° C. before allowing the reaction medium to return to room temperature.

An anhydrous base is obtained having a mass of grafted copolymer of 143.3 g i.e. 71.7% based on the initial reaction mixture.

The obtained solution of copolymer bearing carboxylic functions, polyether grafts and gem-bisphosphonic units, is then formulated by adding 0.5% by weight of oleic amine with 2 moles of ethylene oxide (marketed under the name of NORAMOX O₂ by CECA) and 1.2% by weight of tributylphosphate (antifoam agent).

Finally, the product is diluted with water in order to obtain a 20% dry extract and it is neutralized with sodium hydroxide at pH 7.

The thereby prepared dispersant is ready to use.

Example 7A-C Preparation of Copolymers of the PCP Type Grafted with AHP

Example 6 is repeated but however replacing the gem-bisphosphonic synthon HEDP with the amount of gem-bisphosphonic synthon AHP prepared in Example 2 indicated in Table 2 below.

An anhydrous base is obtained having a mass of grafted copolymer of 144.5 g i.e. 72.6% based on the initial reaction mixture.

The obtained solution of copolymer bearing carboxylic functions, polyether grafts and gem-bisphosphonic units, is then formulated by adding 0.5% by weight of oleic amine with 2 moles of ethylene oxide (marketed under the name of NORAMOX O₂ by CECA) and 1.2% by weight of tributylphosphate (anti foam agent).

Finally, the product is diluted with water in order to obtain a 20% dry extract and it is neutralized with sodium hydroxide at pH 7.

The thereby prepared dispersant is ready to use.

TABLE 2 Reagents for preparing the copolymers of Examples 6-9 Gem-bisphosphonic synthon PCP type Proportion EX. copolymer Type [molar %] Mass [g] 6A EPB 762.013 HEDP 2 145.5 6B EPB 762.014 HEDP 4 143.3 6C EPB 762.015 HEDP 6 141.1 7A EPB 762.022 AHP 2 146.1 7B EPB 762.023 AHP 4 144.5 7C EPB 762.024 AHP 6 142.9 8A EPB 762.034 BHP 2 146.1 8B EPB 762.035 BHP 4 144.6 8C EPB 762.036 BHP 6 142.9 9A EPB 762.013 + HEDP 2 ND EPB 709028 9B EPB 762.014 + HEDP 4 ND EPB 709028 9C EPB 762.015 + HEDP 6 ND EPB 709028

Example 8A-C Preparation of Copolymers of the PCP Type Grafted with BHP

Example 6 is repeated but however by replacing the gem-bisphosphonic synthon HEDP with the amount of gem-bisphosphonic synthon BHP prepared in Example 3 as indicated in Table 2 above.

An anhydrous base is obtained having a mass of grafted copolymer of 144.6 g i.e. 72.73% based on the initial reaction mixture.

The obtained solution of copolymer bearing carboxylic functions, polyether grafts and gem-bisphosphonic units, is then formulated by adding 0.5% by weight of oleic amine with 2 moles of ethylene oxide (marketed under the name of NORAMOX O₂ by CECA) and 1.2% by weight of tributylphosphate (anti foam agent).

Finally, the product is diluted with water in order to obtain a 20% dry extract and it is neutralized with sodium hydroxide at pH 7.

The thereby prepared dispersant is ready for use.

Example 9A-C Preparation of Copolymers of the PCP Type Grafted with HEDP

Example 6 is repeated but however by adding in the final copolymer a proportion of copolymer of the EPB 729.028 type obtained under the operating conditions of Example 4 but only containing carboxylic functions and methoxypolyethyleneglycol with a molar mass of 2,000 g/mol.

The obtained solution of the mixture of copolymers bearing carboxylic functions, polyether grafts and gem-bisphosphonic units, is then formulated by adding 0.5% by weight of oleic amine with 2 moles of ethylene oxide (marketed under the name of NORAMOX O₂ by CECA) and 1.2% by weight of tributylphosphate (anti foam agent).

Finally, the product is diluted with water in order to obtain a 20% dry extract and it is neutralized with sodium hydroxide at pH 7.

The thereby prepared dispersant is ready for use.

C. Evaluation of the Application Properties

1. Water Reducing Power

In order to evaluate the water reducing power of the copolymers according to the invention, mortars were formulated by adding the prepared copolymers to Examples 6 to 9 as a plasticizer.

The composition of the prepared mortar is detailed in Table 3 below. The non-grafted copolymer (Example 4 EPB 662054 and the mixture EPB 762.014+EPB 729.028, respectively) is used as a reference (REF).

The mortar is prepared according to the following procedure:

Two standardized FULCHIRON sands are introduced into the bowl of a PERRIER kneader. After kneading the sands for 30 seconds at a rate of about 140 rpm, the pre-wetting water which represents ⅓ of the total water to be introduced is added within 15 seconds. The mixing is continued for 15 seconds before leaving the mass at rest for 4 minutes. Next, the cement and the limestone filler (origin: ERBRAY provided by MEAC) are introduced and the mixing is then continued for 1 minute before adding the remainder of the mixing water as well as the totality of the admixture within 30 seconds. The kneader is then stopped for a few instants in order to scrape the edges of the kneading bowl to have a proper homogenous mass and mixing is then continued for again 1 minute at a fast rate of 280 rpm.

TABLE 3 Composition of the mortar used for evaluating workability Component Mass [g] CEM I (Le Havre cement 01/10) 624.9 ERBLAY filler 412.1 AFNOR sand 1350 FULCHIRON sand 587.7 Total water 375.1

The workability of the mortars formulated with the copolymers according to the invention was evaluated by measuring the spread diameter (slump flow) according to the procedure described hereafter.

A mold of frustoconical shape without any bottom reproducing the Abrams cone (see standard NF 18-451, 1981) at a scale of 0.5 is filled; in order to carry out spreading, the cone is lifted perpendicularly to the plate by completing a quarter turn. The spreading is measured at 5, 30, 60 and 90 minutes along 2 diameters at 90° with a tape measure. The result of the spreading measurement is the average of the 2 values to within +1-1 mm. The tests were carried out at 20° C.

The dosage of the grafted copolymer is determined so as to attain a target spread comprised between 310 and 330 mm. Unless indicated otherwise, the dosage is expressed in percent by weight based on the total weight of the binder (filler+cement).

The results obtained for the mortars formulated with the copolymers grafted with HEDP of Example 6 are transferred into Table 4 below.

Upon examining the results, it is seen that the grafting with 2 or 4% of HEDP gives the possibility of substantially lowering the dosage (passing from 0.60% to 0.35%) for an equivalent initial spread.

TABLE 4 Spreading of a mortar with an admixture of copolymers of Example 6 Loss of Grafting Dosage Spreading T [mins] fluidity EX. [molar %] [%] 5 30 60 90 120 [%] REF — 0.5 335 325 300 280 245 26.87 REF 4% HEDP 0.5 315 310 290 270 245 22.22 without grafting 6A 2% HEDP 0.35 320 245 190 165 125 60.94 6B 4% HEDP 0.35 340 275 220 195 155 54.41 6C 6% HEDP 0.35 340 225 195 155 125 63.24

It is moreover verified that by simply adding to the control formulation, 4% of HEDP, (EPB 760.020), which is then not grafted to the copolymer, it is not possible to modify the water reducing power of the control grafted copolymer.

Improvement in the water reducing power of the bis-phosphonic grafted copolymers may be explained by a larger affinity for the surface of the cement grains.

The results obtained for the mortars formulated with the AHP-grafted copolymers prepared in Example 7 as described earlier are transferred into Table 5 below.

TABLE 5 Spreading of a mortar with admixture of copolymers of Example 7 Loss of Grafting Dosage Spreading T [mins] fluidity EX. [molar %] [%] 5 30 60 90 120 [%] REF — 0.5 335 335 290 270 245 26.87 REF — 0.5 340 340 320 310 280 17.65 7A 2% AHP 0.35 335 245 215 170 155 53.73 7B 4% AHP 0.35 320 225 175 140 120 62.50 7C 6% AHP 0.35 340 235 200 170 140 58.82

It is seen that by grafting 2, 4 or 6% of AHP, it is also possible to lower the dosage of superplasticizer (passing from 0.50% to 0.35%) for an equivalent initial spread.

The results obtained for the mortars formulated with the BHP-grafted copolymers prepared in Example 8 as described earlier are transferred into Table 6 below.

TABLE 6 Spreading of a mortar with an admixture of copolymers of example 8 Loss of Grafting Dosage Spreading T [mins] fluidity EX. [molar %] [%] 5 30 60 90 120 [%] REF — 0.5 330 330 315 260 245 25.76 REF — 0.4 330 330 270 225 175 46.97 8A 2% BHP 0.4 330 270 245 190 160 51.52 8B 4% BHP 0.4 340 290 265 200 165 51.47 8C 6% BHP 0.35 320 200 160 125 120 62.50

The obtained results show that the grafting of 2 or 4% of BHP also allows lowering of the dosage (passing from 0.5% to 0.4%) for an equivalent initial spread.

With the results presented above, it is possible to conclude that the introduction of bis-phosphonic units on a PCP backbone modifies the water reducing power of the copolymers.

Without intending to be bound by any theory, this observation may be explained by increased affinity of the grafted copolymers for the surface of the cement particles.

2. Improvement in the Water Reducing Power while Maintaining Fluidity

Moreover, it was surprisingly observed that these polymers with gem-bisphosphonate groups give the possibility of significantly improving the water reducing power without degrading the maintenance of rheology on a wide range of concentrations of polyoxyalkylene chains in the copolymer, expressed by the ester level in Table 8.

TABLE 7 Composition of the mortar used for evaluating workability Mortar composition Batch Mixed [g] CEM I 52,5 R SPLC 19/05/2010 800 DURCAL 10 filler ND 120 AFNOR sand ND 1350 Total water ND 300

TABLE 8 Spreading of a mortar with an admixture of copolymers of Example 9 Commercial Dry MPEG dosage dosage Spread [mm] 2000 HEDP Overall SPLC 52,5 R [&] [%] 5 3 60 level level ester level EPB 819019 1.20 0.30 315 315 310 25 0 25 EPB 819012 1.00 0.25 310 320 310 25 4 29 EPB 819027 0.85 0.21 300 295 295 25 8 33 EPB 819035 0.50 0.13 305 275 290 25 12 37 EPB 819036 0.50 0.13 290 275 285 25 16 41

It is seen upon examining Table 8 above that by using an additive including a polyalkoxylated polycarboxylic copolymer grafted with 4% and 8% of HEDP in a cement formulation it is possible to reduce the dosage of superplasticizer with maintaining fluidity over time.

2. Sensitivity to Alkaline Sulfates

In order to evaluate the impact of the presence of alkaline sulfates on the efficiency of the copolymers according to the invention as a superplasticizer, one proceeded with tests with mortars having variable sulfate content.

The content of alkaline sulfates in the mortars was modified by adding powdered potassium sulfate to the cement (0.3 and 0.6% by weight based on the dry/dry weight of the cement). The mortar was then prepared according to the formulation indicated in Table 9 below, by adding to the mixing water, the indicated dosage of reference copolymer.

The spread of these mortars was evaluated as described above.

TABLE 9 Composition of the mortar used for evaluating the sensitivity to sulfates Component Mass [g] CEM I (Le Havre cement 01/10) 624.9 ERBLAY filler 412.1 AFNOR sand 1350 FULCHIRON sand 587.7 Total water 375.1

The obtained results are transferred into Tables 10 and 11 below, respectively. The indicated total sulfate concentration takes into account the level of alkaline compounds initially present in Le Havre cement (LH), evaluated to be 0.25% by weight (dry/dry basis).

It is observed that the referenced superplasticizer dosage required for obtaining a targeted spread is nearly trebled in the presence of an additional 0.6% by weight of alkaline sulfate.

TABLE 10 Effect of the sulfates - reference superplasticizer Added Total K₂SO₄ [% alkaline Grafting by weight sulfates Dosage Spread T [mins] EX. [molar %] of the cement] [% by weight] [%] 5 30 60 90 120 REF — — 0.25 0.5 320 295 240 180 140 REF — 0.3 0.55 0.8 310 305 270 230 200 REF — 0.6 0.85 1.3 325 320 315 300 280

The tests were then repeated by using the copolymer of Example 6B (grafted with 4% of HEDP) in the mortar formulation. The obtained results are summarized in Table 11 below.

TABLE 11 Effect of the sulfates - copolymer of Example 6, constant spread Grafting Added K₂SO₄ Spread T [mins] EX. [molar %] [% by weight] Dosage [%] 5 30 60 90 120 REF — — 0.5 320 295 240 180 140 REF — 0.3 0.8 310 305 270 230 200 REF — 0.6 1.3 325 320 315 300 280 6B 4% (HEDP) — 0.35 310 200 150 110 110 6B 4% (HEDP) 0.3 0.5 340 325 290 260 215 6B 4% (HEDP) 0.6 0.5 265 230 200 170 150

These results demonstrate the interesting effect of the copolymers according to the invention at the level of sensitivity to the presence of alkaline sulfates. Indeed, it is seen that the copolymer according to the invention tolerates much higher alkaline sulfate levels in the cement as compared with the reference plasticizer.

In order to better evaluate the insensitivity to the sulfate ions brought by the bisphosphonic functionalization, the previous tests were repeated, with the same mortar composition, by adding and increasing concentration of potassium sulfate but by imposing constant dosage.

The results obtained for the copolymers of Example 6A and 6B are collected in Table 12 below.

The results demonstrate that functionalization with 4% of HEDP gives the possibility of suppressing the detrimental effect of 0.4% by weight of alkaline sulfate in the cement under the conditions of the test.

Moreover, it is seen that a copolymer grafted with 2% of HEDP in a cement mortar loaded with 0.3% by weight of potassium sulfate has a similar behavior or even a slightly superior behavior in maintaining rheology as that of the reference. In other words, grafting of the reference copolymer with 2% of HEDP gives the possibility of suppressing the detrimental effect of 0.3% by weight of potassium sulfate presence in a cement.

TABLE 12 Effect of the sulfates - copolymers of Example 6, constant dosage Grafting Added K₂SO₄ Spread T [mins] EX. [molar %] [% by weight] Dosage [%] 5 30 60 90 120 REF — — 0.5 310 275 220 170 145 6A 2% (HEDP) — 0.4 340 280 200 155 120 6A 2% (HEDP) 0.3 0.5 320 310 280 230 180 6A 2% (HEDP) 0.6 0.5 225 185 160 140 120 REF — — 0.5 320 300 255 200 160 6B 4% (HEDP) 0.3 0.5 340 325 290 260 215 6B 4% (HEDP) 0.4 0.5 320 300 255 210 175 6B 4% (HEDP) 0.5 0.5 295 270 215 185 160 6B 4% (HEDP) 0.6 0.5 265 230 200 170 150

The use of the copolymers according to the invention as a superplasticizer is therefore less sensitive towards alkaline sulfates in the cements, as compared with the non-grafted copolymer. This observation may be explained by a complexing power of the phosphorate group towards calcium ions which is greater as compared with sulfate ions.

3. Sensitivity to Clays

Superplasticizers are also sensitive to the presence of clays in the compositions, generally in the sands.

In order to evaluate this sensitivity of the copolymers according to the invention, the spreading of mortars formulated with sand polluted with a clay (montmorillonite KSF) was measured and compared with that of a mortar formulated with a clean non-polluted sand.

Unless indicated otherwise, the clay percentage is expressed in percent by dry weight based on the total dry sand, consisting of AFNOR sand and of FULCHIRON sand, the added clay is introduced with the sand before adding pre-wetting water.

The mortars were prepared according to the formulation indicated in Table 7 above, by using the cement with a strong level of alkaline compounds (CEM I 52,5 N cement from Saint Pierre la Cour, marketed by Lafarge) and the copolymer according to Example 9B (mixture of EPB 762.014 grafted with 4% HEDP and of EPB 729.028).

The results of the tests are shown in Table 13 below.

These results show that the studied copolymers according to invention are significantly less sensitive to clay present in the sands, to the extent of widely neutralizing the detrimental effect of 1% by weight of clay (based on dry sand) on the fluidity of the cement composition.

TABLE 13 Clay effect - copolymer of example 9 Added clay* Grafting [% by Spread T [mins] EX. [molar %] weight] Dosage 5 30 60 90 120 REF — — 1.0 315 295 290 285 280 REF — 1 1.0 180 160 145 120 110 REF — 1 1.2 215 180 170 160 150 9B 4% 1 1.0 275 250 240 225 210 (HEDP) 9B 4% 1 1.2 335 320 300 295 285 (HEDP) *The added clay is KSF montmorillonite marketed by ALDRICH

4. Efficiency on Composite Cements

In order to evaluate the robustness of the copolymers according to the invention, the superplasticising effect was studied on composite cements with different composition.

More specifically, a cement was tested, including as a substitution binder, flying ashes (CEM II/A-V cement (Saint Pierre La Cour, marketed by LAFARGE)). The mortars were prepared according to the formulation given in Table 9 and added with admixture with various dosages of copolymer of Example 9B.

The spreading values obtained for these mortars are collected in Table 14 below.

TABLE 14 Effect on flying ash cement Grafting Dosage Spread T [mins] EX. [molar %] [%] 5 30 60 90 120 REF — 1.0 325 315 310 300 260 9B 4% (HEDP) 1.0 360 370 380 380 370 9B 4% (HEDP) 0.8 320 340 345 340 320

The obtained results show that in the presence of flying ashes, the copolymers according to the invention have a higher water reducing power than the reference superplasticizer.

Moreover, it is noted that by reducing the dosage by 20% of the copolymer according to the invention it is possible to obtain a cement composition having a rheological behavior in terms of maintaining fluidity, superior to that of the reference superplasticizer.

On the other hand, a cement including as a substitution binder a slag (CEM III/A 42,5 N-LH PM-ES-CP1 (marketed by Lafarge) of the following composition, was tested:

-   -   Clinker 35% by weight (C3A 8.6%-C3S 60%-C4AF 11)     -   Slag 62% by weight     -   Secondary constituents 3% by weight     -   Gypsum 4.8% by weight.

The mortars were prepared according to the formulation given in Table 9 and added with admixture with different dosages of copolymer of Example 9B.

The spread values obtained for these mortars are collected in Table 15 below.

TABLE 15 Effect on slag cement Grafting Dosage Spread T [mins] EX. [molar %] [%] 5 30 60 90 120 REF — 0.5 325 345 330 300 280 9B 4% (HEDP) 0.5 380 390 380 330 310 9B 4% (HEDP) 0.4 325 320 260 225 190

The obtained results show that in the presence of slag as a substitution binder, the copolymers according to the invention have a higher water reducing power than the reference superplasticizer.

The experimental data above confirm the benefit of the copolymers according to the invention as a superplasticizer for compositions of hydraulic binders. These copolymers actually have a higher water reducing power, low sensitivity to alkaline sulfates and to clays as well as high robustness and good maintenance of rheology in a wide range of ester levels. 

What is claimed is:
 1. A copolymer comprising a main hydrocarbon chain and side groups, wherein the side groups comprise carboxylic groups, polyoxyalkylate groups and gem-bisphosphonate groups, wherein the carboxylic groups of the copolymer fit the formula (III) below: C(O)—ORd  (III) wherein Rd represents H or a C1-C12 alkyl, aryl, alkylaryl or arylalkyl group or an alkali metal, alkaline earth metal or ammonium cation; and the gem-bisphosphonate side groups: fit the formula (IA) below

wherein: L represents a group —NR₄— for binding to a carboxylic group of the main chain wherein R₄ is a hydrogen or a C₁-C₆ alkyl group; X is a C₁-C₂₀ alkylene spacer group optionally substituted; R1 are, independently of each other, hydrogen, or a cation; and R2 is a hydrogen atom, a hydroxyl group or a C₁-C₁₀ alkyl group; or is a result of a grafting with 1-hydroxyethylene-1,1-bisphosphonic acid (HEDP) to carboxylic group of the main chain.
 2. The copolymer according to claim 1, wherein the polyoxyalkylate side groups are bound to the main chain through an ester, ether or amide bond.
 3. The copolymer according to claim 1, wherein the polyoxyalkylate groups are of the formula (II) below: —R _(e) —Z-A  (II) wherein: R_(e) is a C₁-C₁₂ alkylene group, a C═O group, or is absent; and Z is an oxygen atom or a group N—R⁴, wherein R⁴ is a hydrogen, or a C₁-C₆ alkyl group; and A is a group of formula -(QO)_(n)—R³ wherein: Q represents an alkylene group with 2 to 4 carbon atoms or a mixture of these alkylene groups; n is an integer varying from 1 to 500; and R³ represents a hydrogen atom or a C₁-C₁₂ alkyl, aryl, alkylaryl, or arylalkyl group.
 4. The copolymer according to claim 3, wherein, in the polyoxyalkylate groups of formula (II), A is a group of formula -(QO)_(n)—R³ wherein R³ is a methyl.
 5. The copolymer according to claim 1, wherein the carboxylic groups fit the formula (III) below: —C(O)—O-R _(d)  (III) wherein: R_(d) represents.
 6. An admixture for suspensions of mineral particles comprising the copolymer according to claim 1, as a solution in a suitable solvent.
 7. The admixture according to claim 6, comprising 1 to 50% by weight of copolymer based on the total weight.
 8. A method of fluidifying suspensions of mineral particles comprising adding to said suspensions of mineral particles the copolymer according to claim
 1. 9. A method of maintaining workability of hydraulic binders comprising adding to said hydraulic binders the copolymer according to claim
 1. 10. A method of reducing the sensitivity of hydraulic compositions to clays comprising adding to said hydraulic compositions the copolymer according to claim 1 in the presence of clays.
 11. A composition of mineral particles comprising the copolymer according to claim
 1. 12. The copolymer according to claim 1, wherein X is a C₁-C₆ alkylene group.
 13. The copolymer according to claim 1, wherein R1 is a hydrogen.
 14. The copolymer according to claim 1, wherein R1 is an alkali metal, an alkaline earth metal, or an ammonium cation.
 15. The copolymer according to claim 1, wherein the gem-bisphosphonate groups of the copolymer is a result of a grafting with a compound selected from the group consisting of 1-hydroxy-3-amino-propylene-1,1-bisphosphoic acid (AHP) and 1-hydroxy-4-amino-butylène-1,1-bisphosphonic acid (BHP) to carboxylic group of the main chain.
 16. A method for preparing a copolymer comprising a main hydrocarbon chain and side groups, wherein the side groups comprise carboxylic groups, polyoxyalkylate groups and gem-bisphosphonate groups, comprising: (i) polymerizing a monomer bearing a carboxylic group, in the presence of a monomer bearing a polyoxyalkylate group; and (ii) grafting the obtained polymer with a reactive gem-bisphosphonate compound.
 17. A method of reducing the sensitivity of hydraulic binders to alkaline sulfates comprising adding to said hydraulic binders a copolymer comprising a main hydrocarbon chain and side groups, wherein the side groups comprise carboxylic groups, polyoxyalkylate groups and gem-bisphosphonate groups in the presence of alkaline sulfates.
 18. An admixture for suspensions of mineral particles comprising a copolymer comprising a main hydrocarbon chain and side groups, wherein the side groups comprise carboxylic groups, polyoxyalkylate groups and gem-bisphosphonate groups, wherein the admixture is 10 to 30% by weight of the copolymer based on total weight. 